The invention relates to a sandwich panel and to a method for producing such sandwich panels.
The interior of an aircraft is predominantly formed of fiber-reinforced plastic materials. For floor lining panels and wall lining panels, for example, in many cases sandwich panels with a core structure and cover layers that cover the aforesaid on both sides are used, which sandwich panels feature great mechanical stiffness while being of a lightweight design. Frequently the core structure comprises a multitude of honeycomb cells whose walls, for example comprising a polyamide paper impregnated with a phenolic resin, are coated or impregnated. The cover layers are, for example, semi-finished fiber products, so-called prepregs, that are preimpregnated with an uncured thermoplastic or duroplastic synthetic matrix, which prepregs in the production of the sandwich panel are pressed as a compound structure with the core structure and cure as a result of the application of pressure and temperature. In order to create local reinforcements in sandwich panels, for example in order to form force transmission points, usually inserts are inserted into cutouts in the core structure and are pressed, together with the core structure and the cover layers, with the application of temperature, to form the sandwich panel. The inserts are, for example, cured fiber composite components, while the cover layers are, for example, uncured semi-finished fiber composite products, such as so-called prepregs, that are preimpregnated with a resin matrix. In order to avoid uneven features or fluctuations in the thickness of the sandwich panel the at least one insert must comprise an extension that corresponds to a cover layer distance. Likewise, in the case of a multitude of inserts, their extension must not vary. In a known production method the compound structure is arranged between two rigid pressure plates and is pressed by means of the aforesaid. If the at least one insert is too large, it is not possible to optimally connect the core structure in the immediate vicinity of the insert to the cover layers. In the surroundings of the at least one insert a so-called pressure shadow is formed. In contrast to this, if the at least one insert is too small, in turn connection problems relating to the at least one insert can occur because only the core structure is subjected to the command pressure.
From EP 1 024 301 A2 a variable-thickness or variable-height insert is known that comprises two components which after the production of a sandwich panel are inserted in sections into a through-hole of the sandwich panel. The insert components in each case comprise a flange for resting externally against the sandwich panel, and in each case a bottom that points radially inwards. The bottoms comprise an opening for receiving a screw for connecting the sandwich panel to a surrounding structure. The insert components are bonded to the sandwich panel by way of an adhesive, wherein in the case in which the sandwich panel is thicker than the extension of the insert components between their flanges, the adhesive enters the gap between the bottoms and cures.
From U.S. Pat. No. 5,093,957 a sandwich panel is known whose at least one insert also comprises a multi-component design, with the insert after production of the sandwich panel being inserted into a cutout of the sandwich panel. After the production of the sandwich panel the inserts are inserted into a through-hole of the sandwich panel, wherein each of said inserts rests by a flange against the exterior of the sandwich panel. In each case a tubular projection extends from each flange, wherein the projections are designed so that they can be slid into each other. Fixing the insert components relative to each other and in the sandwich panel takes place by means of an adhesive that surrounds the projections on the external circumference.
U.S. Pat. No. 3,716,092 shows a sandwich panel with a multi-component insert that after the production of the sandwich panel is inserted into a one-sided cutout of the sandwich panel. The insert comprises a bottom component with a tubular projection that over its entire surface rests against the inside of a bottom cover layer, and a top component with a tubular projection that in the installed state finishes off flush with the outside of a top cover layer. During installation the bottom insert is inserted into the one-sided recess of the sandwich panel, and then the top insert component is slid onto the bottom insert until it finishes off so as to be flush with the top cover layer. In this process an adhesive is laterally pressed out of a space between the insert components. A quantity of adhesive remaining between the insert component cures.
Further prior art is known from U.S. Pat. No. 4,399,642, U.S. Pat. No. 2,607,447A, U.S. Pat. No. 4,981,735, GB 921 569 and DE 10 2009 010 961 A1.